/* ec_dh.c - TinyCrypt implementation of EC-DH */

/*
 * Copyright (c) 2014, Kenneth MacKay
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *  * Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 *  * Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

/*
 *  Copyright (C) 2017 by Intel Corporation, All Rights Reserved.
 *
 *  Redistribution and use in source and binary forms, with or without
 *  modification, are permitted provided that the following conditions are met:
 *
 *    - Redistributions of source code must retain the above copyright notice,
 *     this list of conditions and the following disclaimer.
 *
 *    - Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 *    - Neither the name of Intel Corporation nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 *  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 *  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 *  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 *  ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 *  LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 *  CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 *  SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 *  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 *  CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 *  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 *  POSSIBILITY OF SUCH DAMAGE.
 */
#include <tinycrypt/constants.h>
#include <tinycrypt/ecc.h>
#include <tinycrypt/ecc_dh.h>
#include <tinycrypt/utils.h>
#include <string.h>

#if default_RNG_defined
static uECC_RNG_Function g_rng_function = &default_CSPRNG;
#else
static uECC_RNG_Function g_rng_function = 0;
#endif

int uECC_make_key_with_d(uint8_t *public_key, uint8_t *private_key,
                         unsigned int *d, uECC_Curve curve)
{

    uECC_word_t _private[NUM_ECC_WORDS];
    uECC_word_t _public[NUM_ECC_WORDS * 2];

    /* This function is designed for test purposes-only (such as validating NIST
     * test vectors) as it uses a provided value for d instead of generating
     * it uniformly at random. */
    memcpy (_private, d, NUM_ECC_BYTES);

    /* Computing public-key from private: */
    if (EccPoint_compute_public_key(_public, _private, curve)) {

        /* Converting buffers to correct bit order: */
        uECC_vli_nativeToBytes(private_key,
                               BITS_TO_BYTES(curve->num_n_bits),
                               _private);
        uECC_vli_nativeToBytes(public_key,
                               curve->num_bytes,
                               _public);
        uECC_vli_nativeToBytes(public_key + curve->num_bytes,
                               curve->num_bytes,
                               _public + curve->num_words);

        /* erasing temporary buffer used to store secret: */
        _set_secure(_private, 0, NUM_ECC_BYTES);

        return 1;
    }
    return 0;
}

int uECC_make_key(uint8_t *public_key, uint8_t *private_key, uECC_Curve curve)
{

    uECC_word_t _random[NUM_ECC_WORDS * 2];
    uECC_word_t _private[NUM_ECC_WORDS];
    uECC_word_t _public[NUM_ECC_WORDS * 2];
    uECC_word_t tries;

    for (tries = 0; tries < uECC_RNG_MAX_TRIES; ++tries) {
        /* Generating _private uniformly at random: */
        uECC_RNG_Function rng_function = uECC_get_rng();
        if (!rng_function ||
                !rng_function((uint8_t *)_random, 2 * NUM_ECC_WORDS * uECC_WORD_SIZE)) {
            return 0;
        }

        /* computing modular reduction of _random (see FIPS 186.4 B.4.1): */
        uECC_vli_mmod(_private, _random, curve->n, BITS_TO_WORDS(curve->num_n_bits));

        /* Computing public-key from private: */
        if (EccPoint_compute_public_key(_public, _private, curve)) {

            /* Converting buffers to correct bit order: */
            uECC_vli_nativeToBytes(private_key,
                                   BITS_TO_BYTES(curve->num_n_bits),
                                   _private);
            uECC_vli_nativeToBytes(public_key,
                                   curve->num_bytes,
                                   _public);
            uECC_vli_nativeToBytes(public_key + curve->num_bytes,
                                   curve->num_bytes,
                                   _public + curve->num_words);

            /* erasing temporary buffer that stored secret: */
            _set_secure(_private, 0, NUM_ECC_BYTES);

            return 1;
        }
    }
    return 0;
}

int uECC_shared_secret(const uint8_t *public_key, const uint8_t *private_key,
                       uint8_t *secret, uECC_Curve curve)
{

    uECC_word_t _public[NUM_ECC_WORDS * 2];
    uECC_word_t _private[NUM_ECC_WORDS];

    uECC_word_t tmp[NUM_ECC_WORDS];
    uECC_word_t *p2[2] = {_private, tmp};
    uECC_word_t *initial_Z = 0;
    uECC_word_t carry;
    wordcount_t num_words = curve->num_words;
    wordcount_t num_bytes = curve->num_bytes;
    int r;

    /* Converting buffers to correct bit order: */
    uECC_vli_bytesToNative(_private,
                           private_key,
                           BITS_TO_BYTES(curve->num_n_bits));
    uECC_vli_bytesToNative(_public,
                           public_key,
                           num_bytes);
    uECC_vli_bytesToNative(_public + num_words,
                           public_key + num_bytes,
                           num_bytes);

    /* Regularize the bitcount for the private key so that attackers cannot use a
     * side channel attack to learn the number of leading zeros. */
    carry = regularize_k(_private, _private, tmp, curve);

    /* If an RNG function was specified, try to get a random initial Z value to
     * improve protection against side-channel attacks. */
    if (g_rng_function) {
        if (!uECC_generate_random_int(p2[carry], curve->p, num_words)) {
            r = 0;
            goto clear_and_out;
        }
        initial_Z = p2[carry];
    }

    EccPoint_mult(_public, _public, p2[!carry], initial_Z, curve->num_n_bits + 1,
                  curve);

    uECC_vli_nativeToBytes(secret, num_bytes, _public);
    r = !EccPoint_isZero(_public, curve);

clear_and_out:
    /* erasing temporary buffer used to store secret: */
    _set_secure(p2, 0, sizeof(p2));
    _set_secure(tmp, 0, sizeof(tmp));
    _set_secure(_private, 0, sizeof(_private));

    return r;
}
